In the prior art, there have been proposed a variety of dot-matrix type organic EL panels and their driving methods, as disclosed in Patent Document 1. In this organic EL panel: a plurality of anode lines (as will be called the “drive lines”) formed of a conductive transparent film such as ITO are formed on a light-transmitting substrate in a stripe shape; an organic layer is formed on the back of the drive lines; a plurality of cathode lines (as will be called the “scanning lines”) of an evaporated metal film of aluminum or the like are formed on the back of the organic layer to intersect the drive lines at the right angle; and the drive lines and the scanning lines clamp the aforementioned organic layer. The organic EL panel thus formed is noted as such a display in place of the liquid crystal display as has a lower power consumption, a higher display quality and a smaller thickness.
Patent Document 1: Japanese Patent No. 3,314,046.
The organic EL display device includes an organic EL panel 1, a cathode drive circuit 2, an anode drive circuit 3, a control unit 4, and a reset circuit 5 (as referred to FIG. 6).
In the organic EL panel 1, pixels E11 to Emn are arranged in a matrix state. These pixels E11 to Emn are disposed at intersections between a plurality of scanning lines S1 to Sm in the longitudinal direction and a plurality of drive lines D1 to Dn in the transverse direction orthogonal to the scanning lines S1 to Sm. The pixels E11 to Emn are expressed by an equivalent circuit (as referred to FIG. 7) composed of a diode and a condenser arranged in parallel. In order to prevent the illustration from being complicated, the pixels E11 to Emn to luminesce are shown with only diodes, and the pixels E11 to Emn not to luminesce are shown with only condensers in FIG. 8 and FIG. 9.
The cathode drive circuit 2 is provided with a plurality of scanning switches 21 to 2m corresponding to the individual scanning lines S1 to Sm. On the basis of the control signals of the control unit 4, the scanning switches 21 to 2m connect the individual scanning lines S1 to Sm selectively to the unselected potential Vb or the earth potential (0V).
The anode drive circuit 3 includes constant current sources 30 for feeding drive currents individually to the individual drive lines D1 to Dn, and drive switches 31 to 3n capable of connecting the individual drive currents from the constant current sources 30 to the individual drive lines D1 to Dn. The switching of each of the drive switches 31 to 3n is determined on the basis of the control signal from the control unit 4.
The control unit 4 outputs the control signals individually to the cathode drive circuit 2 and the anode drive circuit 3, and selectively turn ON/OFF the scanning switches 21 to 2m and the drive switches 31 to 3n corresponding to the scanning lines S1 to Sm and the drive lines D1 to Dn necessary for causing the pixels E11 to Emn to luminesce.
The reset circuit 5 is composed of a plurality of reset switches 50 individually connected with the drive lines D1 to Dn. These reset switches 50 connect the drive lines D1 to Dn to the earth potential, while next scanning lines S1 to Sm are being selected after arbitrary scanning lines S1 to Sm were selected by the scanning switches 21 to 2m, thereby to release the charges from the pixels E11 to Emn. The period, for which the electric charge stored in the pixels E11 to Emn is released by the reset circuit 5, is called the “reset period”. For this reset period, not only the drive lines D1 to Dn but also the scanning lines S1 to Sm are connected to the earth potential.
The control circuit 4 turns ON the scanning switches 21 to 2m sequentially to select the scanning lines S1 to Sm sequentially, and turns ON/OFF the individual drive switches 31 to 3n to display characters and drawings on the organic EL panel 1.